Diffuse Reflectance Infrared Fourier Transform Research Articles

A Novel Non-Fullerene D-A Interface with Two Asymmetrical Electron Acceptors Facilitates Charge and Energy Transfer for Effective Carbon Dioxide Reduction.

Converting carbon dioxide (CO2) into high-value chemicals using solar energy remains a formidable challenge. In this study, the CSC@PM6:IDT6CN-M:IDT8CN-M non-fullerene small-molecule organic semiconductor is designed with highly efficient electron donor-acceptor (D-A) interface for photocatalytic reduction of CO2. Atomic Force Microscope and Transmission Electron Microscope images confirmed the formation of an interpenetrating fibrillar network after combination of donor and acceptor. The CO yield from the CSC@PM6:IDT6CN-M:IDT8CN-M reached 1346µmolg-1h-1, surpassing those of numerous reported inorganic photocatalysts. The D-A structure effectively facilitated charge separation to enable electrons transfer from the PM6 to IDT6CN-M:IDT8CN-M. Meanwhile, attributing to the dipole moments of the strong intermolecular interactions between IDT6CN-M and IDT8CN-M, the intermolecular forces are enhanced, and laminar stacking and π-π stacking are strengthened, thereby reinforcing energy transfer between acceptor molecules and significantly enhanced charge separation. Moreover, the strong internal electric field in the D-A interface enhanced the excited state lifetime of PM6:IDT6CN-M:IDT8CN-M. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that carboxylate (COOH*) is the predominant intermediate during CO2 reduction, and possible pathways of CO2 reduction to CO are deduced. This study presents a novel approach for designing materials with D-A interface to achieve high photocatalytic activity.

Nanocube-shaped In2O3@TiO2 core-shell based chemiresistive-type sensors for formaldehyde detection at room temperature

In2O3@TiO2 core-shell nanocubes were successfully prepared via hydrothermal method and subsequent water bath method. The characterization results show that the size of the In2O3@TiO2 nanocomposites is 250–350 nm. The In2O3@TiO2 nanocomposites based sensor presents excellent sensing response to formaldehyde at ppb level. The response of In2O3@TiO2 nanocomposites based sensor to 1 ppm formaldehyde is about 5.3 at room temperature under UV activation, which is three times higher than that of the pure In2O3 based sensor. The response/recovery time of In2O3@TiO2 nanocomposites based sensor are 24 s and 52 s, respectively. The involved chemical reactions activated by UV had been investigated by in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). This work proves that core-shell nanocubes combined with UV activation could significantly enhance the sensing properties of the sensors.

Gas discrimination and concentration prediction based on sensing features deriving from molecular interfacial interactions

The chemresistive sensing process derives from the interfacial interactions between the gaseous molecule and the sensing material’s surface. However, the deeper understanding of gas-solid interfacial interactions during gas sensing is still a formidable challenge. In this study, we combine in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ Raman spectroscopy to systemically investigate interfacial sensing reactions, adsorption-desorption processes of surface species and structural evolutions of cobalt oxide. Interestingly, we discover that the different electron densities of Co−O bonds are responsible for the changes in the sensor’s resistance among three kinds of target analytes, which reveals the origin of temperature/analyte-dependent sensing features. Furthermore, these features are utilized to enable sensors capable of discriminating volatile organic compounds and predicting gas concentrations by algorithm analysis. Our research provides molecular insights into the understanding of gas-solid interfacial interactions during the gas-sensing process and offers a valuable strategy for designing sensing materials with outstanding performance.

Spectroscopic analysis of Pu-bearing compounds in double-walled cells

Spectroscopic analysis of radiological materials has been historically limited to radiological labs with older or less advanced scientific instrumentation. The development of double-walled cells (DWCs) at the Savannah River National Laboratory (SRNL) has enabled Pu-bearing compounds to be removed from radiological laboratories and studied in our radiologically clean spectroscopy laboratory with state-of-the-art instrumentation. In this manuscript, we discuss the contributions of DWCs that have allowed the application of Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), diffuse reflectance spectroscopy (DRS) in the shortwave infrared, and gamma spectroscopy at SRNL. Significant advances have been made in the understanding of the thermal decomposition of Pu(III) and Pu(IV) oxalates, alpha-induced damage to the PuO2 crystal lattice, and the effect of calcination temperatures on the quality of PuO2. These techniques have enabled methods to conduct PuO2 age dating since last calcination and estimate the calcination temperature with Raman spectroscopy and DRS. Additional spectroscopic information measured with DRIFTS has enabled the observation of the evolution of carbon species with calcination temperature, while gamma spectroscopy provides information on age dating since last purification.

Mineralogical differences between seam and prism material in loess‐derived fragipans in western Kentucky

AbstractFragipan horizons are common diagnostic subsurface features typically identified by their dense, brittle nature under field conditions. Fragipan horizons are often hypothesized to contain various silicate bonding agents, including phyllosilicates, amorphous aluminosilicates/silica, and silica sorbed to iron oxyhydroxides. However, the association of silica (Si) with other minerals in these horizons remains uncertain. To fill this knowledge gap, we sampled the prism and seam material of four loess‐derived fragipan horizons in western Kentucky. We characterized and compared the clay mineral composition of the prism and seam material using X‐ray diffraction (XRD), selective extractions, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Fragipan prism and seam material exhibited a mixed clay mineralogy comprised of vermiculite, mixed layer minerals (hydroxyl‐interlayered vermiculite), illite, kaolinite, and quartz. We identified goethite in fragipan prisms in much greater quantities when compared to seam material, confirmed by both XRD and DRIFTS and corroborated by higher dithionite‐extractable iron in prisms. DRIFT spectra showed a peak near 3180 cm−1 assigned to OH‐stretching mode of goethite, which was prominent in prism materials. Goethite 110 XRD peak positions were negatively correlated to dithionite‐extractable aluminum (Al) and Si content of the prism material, which may suggest greater Si sorbed to the surfaces of Al‐substituted goethite. These results demonstrate the potential importance of Al‐substituted goethite in fragipan prisms and provide insight about possible associations with Si.

Unveiling the significant promoting effect of SO2 on Ir/SiO2 catalyst for the CO-SCR of NOx in the presence of O2

Selective catalytic reduction of NOx by CO (CO-SCR) in the presence of O2 is challenging because in this process CO is prone to being oxidized by O2, thus inhibiting NOx reduction by CO. Furthermore, SO2 typically leads to the deactivation of the CO-SCR catalyst. Herein, a significant promoting effect of SO2 on Ir/SiO2 catalyst for the CO-SCR of NOx in the presence of O2 is reported. In-situ X-ray Absorption Fine Structure (XAFS) and X-ray photoelectron spectroscopy (XPS) analysis showed that SO2 does not affect the chemical nature of Ir0 under reaction conditions. However, SO2 can be oxidized to sulfate and deposit on the catalyst surface. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that the presence of SO2 can inhibit the CO + O2 reaction, thus leaving more CO available to reduce NOx over the active Ir0 sites. As a result, the reduction of NOx is remarkably promoted even in the presence of O2 and SO2.

0D/3D heterostructure of perovskite Cs2CuBr4 quantum dots/Bi2O3 microflower as a step-scheme photocatalyst for enhanced CO2 reduction

Exploring highly-efficient photocatalytic materials to convert CO2 into clean energy fuels is of great significance. Herein, lead-free perovskite Cs2CuBr4 quantum dots (QDs) were loaded onto Bi2O3 microflower to construct a 0D/3D heterostructure of Cs2CuBr4/Bi2O3 (CCB/Bi2O3) for photocatalytic CO2 reduction reaction (CO2 RR). The developed 0D/3D CCB/Bi2O3 heterostructure exhibited dramatically enhanced CO2 RR activity, with an electron consumption rate (Relectron) up to 322.12 μmol g−1h−1, which was 3.16 folds that of pure Cs2CuBr4 QDs. The improvement of CO2 RR activity was originated from the promoted carrier separation and transfer, as well as retainment of strongly reducing electrons induced by the step-scheme electron transfer mode, as authenticated by in-situ X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and density function theory (DFT) calculation. The CO2 RR pathway was unveiled by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The innovation of perovskite QDs-based step-scheme heterostructures can throw inspiration on designing high-performance photocatalysts applied in artificial photosynthesis.

The pivotal role of oxygen vacancy and surface hydroxyl in the adsorption and activation of CO2 on ceria-zirconia mixed oxide

Ceria-zirconia mixed metal oxide along with pure ceria and zirconia were prepared by the co-precipitation method and characterized by N2-Physisorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), CO-TPR with mass spectroscopy (CO-TPR/MS), oxygen storage capacity (OSC), CO and CO2-temperature programmed desorption with MS (TPD/MS), Raman spectroscopy, XPS, and diffuse reflectance infrared Fourier transform Spectroscopy (DRIFTS) techniques. Furthermore, Density Functional Theory (DFT) calculations were performed to acquire molecular insights into the role of oxygen vacancies and surface hydroxyl species in CO2 adsorption and subsequent activation. Our experimental and theoretical results corroborated the fact that the incorporation of zirconium ions into the ceria matrix enhanced the overall CO2 adsorption and activation by forming thermally stable surface species, which were eventually detected by DRIFTS. Additionally, DFT calculations revealed the oxygen vacancy mediated change in the electronic structure of ceria-zirconia mixed oxide, which had been argued to improve its catalytic activity. Furthermore, the oxygen vacancy formation energy (OVFE), oxygen storage capacity (OSC) and CO2 adsorption energies were correlated to augment the importance of these properties.

Chemical Composition and FTIR Analysis of Acetylated Turkey Oak and Pannonia Poplar Wood

In this research, acetylation was applied under industrial conditions to improve the properties of Turkey oak and Pannonia poplar wood. Both species are potential “climate winners” in Hungary, yet they are currently underused due their low durability and poor dimensional stability. The acetylation modification process may be a suitable method to improve their properties. In order to verify the effectiveness of the process, comparative chemical analyses (cellulose, hemicelluloses, lignin, extractives, ash, buffering capacity, and pH) of the untreated and acetylated heartwood and sapwood were carried out for both species for the first time. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was also used to support the evaluation of the chemical analyses. The weight percent gain was 11.54% for poplar and 0.94% for Turkey oak, indicating poor treatment efficiency for the latter. The cellulose, hemicelluloses, and lignin contents changed significantly in poplar, with the highest change (+81%) induced by acetylating the hemicelluloses. Only the alpha-cellulose content decreased significantly in Turkey oak, presumably due to the degradation of the non-crystalline part of the cellulose. Acetylation may improve the resistance of Pannonia poplar against moisture, weather, decay, and wood-boring insects, but the process parameters need to be optimized in order to prevent degradation and discoloration in poplar. Turkey oak was found to be less suitable for acetylation due to its low permeability and tendency to crack.

Experimental and computational study on removal of nitric oxide using NH2-MIL-125: Revisiting removal mechanism

The NH2-MIL-125 (NM-125) or modified NM-125 materials are used for photocatalytic removal of nitric oxide (NO). Most researchers attributed few NO2 emission during NO photocatalysis to high selectivity towards the formation of nitrate ions due to the neglect of the principle of electroneutrality and pore structure of NM-125. This may cause misleading photocatalytic mechanism of NO removal. Herein, this work proposes a new mechanism behind NO removal using NM-125 based on experimental investigations and theoretical calculations. First, experimentally, the highest NO removal efficiency of 88.54 % with negligible NO2 emission occurs at the anhydrous condition. In addition, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements verify the presence and accumulation of NO2 as product during photocatalytic conversion of NO. Furthermore, density functional theory (DFT) calculations and grand canonical Monte Carlo (GCMC) computations demonstrate that there exist strong interactions between NO2 and -NH2 group within pores. Few NO2 is detected during experiments is probably due to its subsequent adsorption in the pores of NM-125. The new NO removal mechanism including photocatalytic conversion NO into NO2 and subsequent NO2 adsorption in the pores of NM-125 is thus proposed. This work provides a deeper insight into photocatalytic NO removal over NM-125 and its variants.

Si4Al2O2N6 regulating chemical states of Co catalyst for improved hydrogen production from ethanol steam reforming

Tuning the metal-support interaction is a general strategy of regulating the chemical state of catalytic active site for high-efficiency hydrogen production from ethanol steam reforming (ESR) reaction. In this work, a Co catalyst supported on the Si4Al2O2N6 solid solution of Si3N4 and Al2O3 (Co/Si4Al2O2N6) has been developed to effectively catalyze ESR reaction. Our results demonstrate that the Co/Si4Al2O2N6 catalyst exhibits remarkably improved performances as compared with the Co/Si3N4 and Co/Al2O3 catalysts. In the Co/Si4Al2O2N6-catalyzed ESR reaction, ethanol conversion of 97 % has been achieved with hydrogen yield reaching 73 %. Long-time catalytic experiment manifests the Co/Si4Al2O2N6 catalyst possesses excellent durability. X-ray photoelectron spectroscopy (XPS) studies reveal that the enhanced metal-support interaction (MSI) and charge transfer from Si4Al2O2N6 support to Co species in the Co/Si4Al2O2N6 catalyst confer lower valence state on the Co catalyst supported on Si4Al2O2N6, thus promoting the C–C bond cleavage capability, leading to high C1 product yield and boosting the hydrogen-production efficiency. The catalytic mechanism studies explored by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveal that the Co/Si4Al2O2N6 exhibits a remarkable preference for C1 products over the Co/Si3N4 and Co/Al2O3 catalysts at low reaction temperature, thus resulting in high hydrogen-production efficiency with excellent catalytic durability.

The photo-decomposition and self-restructuring dynamic equilibrium mechanism of Cu2(OH)2CO3 for stable photocatalytic CO2 reduction

Developing suitable photocatalysts and understanding their intrinsic catalytic mechanism remain key challenges in the pursuit of highly active, good selective, and long-term stable photocatalytic CO2 reduction (PCO2R) systems. Herein, monoclinic Cu2(OH)2CO3 is firstly proven to be a new class of photocatalyst, which has excellent catalytic stability and selectivity for PCO2R in the absence of any sacrificial agent and cocatalysts. Based on a Cu2(OH)213CO3 photocatalyst and 13CO2 two-sided 13C isotopic tracer strategy, and combined with in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and density functional theory (DFT) calculations, two main CO2 transformation routes, and the photo-decomposition and self-restructuring dynamic equilibrium mechanism of Cu2(OH)2CO3 are definitely revealed. The PCO2R activity of Cu2(OH)2CO3 is comparable to some of state-of-the-art novel photocatalysts. Significantly, the PCO2R properties can be further greatly enhanced by simply combining Cu2(OH)2CO3 with typical TiO2 to construct composites photocatalyst. The highest CO and CH4 production rates by 7.5 wt% Cu2(OH)2CO3-TiO2 reach 16.4 μmol g−1h−1 and 116.0 μmol g−1h−1, respectively, which are even higher than that of some of PCO2R systems containing sacrificial agents or precious metals modified photocatalysts. This work provides a better understanding for the PCO2R mechanism at the atomic levels, and also indicates that basic carbonate photocatalysts have broad application potential in the future.

Facet-Dependent Photocatalytic Behavior of Rutile TiO2 for the Degradation of Volatile Organic Compounds: In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy and Density Functional Theory Investigations.

In this study, a custom rutile titanium dioxide (TiO2) photocatalyst with a single exposed surface was utilized to investigate the facet-dependent photocatalytic mechanism of toluene. The degradation of toluene was dynamically monitored using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technology coupled with theoretical calculations. The findings demonstrated that the photocatalytic degradation rate on the TiO2 (001) surface was nearly double that observed on the TiO2 (110) surface. This remarkable enhancement can be attributed to the heightened stability in the adsorption of toluene molecules and the concurrent reduction in the energy requirement for the ring-opening process of benzoic acid on the TiO2 (001) surface. Moreover, the TiO2 (001) surface generated a greater number of reactive oxygen species (ROS), thereby promoting the separation of photogenerated charge carriers and concurrently diminishing their recombination rates, amplifying the efficiency of photocatalysis. This research provides an innovative perspective for a more comprehensive understanding of the photocatalytic degradation mechanism of TiO2 and presents promising prospects for significant applications in environmental purification and energy fields.

PdCu alloy anchored defective titania for photocatalytic conversion of carbon dioxide into methane with 100% selectivity

The photoreduction of CO2 into CH4 with simultaneous high activity and selectivity is a promising strategy to increase energy supply and alleviate global warming. However, the absence of the active sites that is responsible for the adsorption and activation of CO2 and the generation of CO and H2 via side reactions often lead to poor efficiency and low selectivity of the catalyst. Herein, Cu, Pd, and PdCu metal clusters cocatalyst-anchored defective TiO2 nanotubes (Cu/TiO2-SBO, Pd/TiO2-SBO, and Pd1Cu1/TiO2-SBO) were designed via a simple solution impregnation reduction and applied for photocatalytic conversion of CO2 to CH4. The Pd1Cu1/TiO2-SBO photocatalyst exhibits excellent catalytic performance among the other catalysts for photoreduction of CO2 into CH4. More interestingly, the product selectivity of CH4 reaches up to 100% with a rate of 25 µmol g−1 h−1. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) simulations indicate that the main reasons for the high selectivity of CH4 are attributed to the PdCu alloy and oxygen vacancies, which jointly enhance the photoinduced carrier separation and lower energy barriers of key intermediates. Moreover, due to the tunable d-band center of the Cu site in the PdCu alloy, the generated intermediates can be well prevented from poisoning and promoted to participate in further reactions. Hopefully, the current study will provide insight into the development of new, highly selective photocatalysts for the visible light-catalytic reduction of CO2 into CH4.

Highly efficient CO2 hydrogenation to methanol over Cu–Ce1-xZrxO2 catalysts prepared by an eco-friendly and facile solid-phase grinding method

In this study, a series of Cu–Ce1-xZrxO2 (x = 0, 0.2, 0.5, 0.8, 1) catalysts were prepared by an eco-friendly and facile solid-phase grinding method. The effect of different Ce/Zr molar ratios on the performance of Cu–Ce1-xZrxO2 catalysts for CO2 hydrogenation to methanol was investigated. The results showed that the Cu–Ce0.5Zr0·5O2 catalyst had the best catalytic performance, with CO2 conversion of 15.2 % and methanol yield of 7.5 % at GHSV = 3600 mL/(gcat·h)); when GHSV was increased to 20,000 mL/(gcat·h), the space-time yield of methanol reached 270.8 gCH3OH/(kgcat·h). X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption-desorption, N2O chemisorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by H2 (H2-TPR), and temperature programmed desorption (H2-TPD, CO2-TPD) techniques were used to characterize the catalysts, and the higher reactivity of Cu–Ce0.5Zr0·5O2 can be attributed to more Cu0 species, defect oxygen and basic sites. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) results revealed that the hydrogenation of CO2 to methanol occurred through the formate intermediate pathway. This work proposed an eco-friendly and facile method for the preparation of high-performance Cu-based catalysts and the systematic study provided a deep insight for the development of high-performance Cu-based catalysts for methanol synthesis from CO2 hydrogenation.

Mechanism of photocatalytic CO2 methanation on ultrafine Rh nanoparticles.

Selective hydrogenation of CO2 to yield CH4 relies on the appropriate catalysts that can facilitate the cleavage of CO bonds and dissociative adsorption of H2. Ultrafine Rh nanoparticles loaded on silica nanospheres were used as a class of photocatalysts to significantly improve the selectivity and reaction rate of producing CH4 from the mixture of CO2 and H2 under the illumination of a broadband visible light source. The intense light scattering resonances in the silica nanospheres generate strong electric fields near the silica surface to enhance the light absorption power in the supported ultrafine Rh nanoparticles, promoting the efficiency of hot electron generation in the Rh nanoparticles. The interaction of the hot electrons with the adsorbate species on the Rh nanoparticle surface weakens the C-O bond to facilitate the deoxygenation of CO2, favoring the production of CH4 with a unity selectivity at a faster rate in the presence of surface adsorbed hydrogen (H*). The systematic studies on reaction kinetics and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy under different conditions, including various temperatures, illumination powers, and feeding gas compositions, reveal the reaction mechanism responsible for CO2 methanation and the role of photoillumination.

Mechanistic understanding of the thermal-assisted photocatalytic oxidation of methanol-to-formaldehyde with water vapor over Pt/SrTiO3.

Anaerobic thermal-assisted photocatalytic methanol conversion in the gas phase in the presence of water vapor has been suggested as an interesting way to generate formaldehyde as a valuable coupled product in addition to H2 production. Here, the reaction mechanism and photocatalyst deactivation are investigated in detail using in situ diffuse reflectance infrared fourier transform (DRIFTS) and electron paramagnetic resonance (EPR) spectroscopy. EPR shows that paramagnetic oxygen vacancies are not involved in the reaction mechanism over undoped SrTiO3. Instead, on an optimized 0.1 wt% Pt/SrTiO3 photocatalyst, methoxy species are formed by dissociative adsorption of methanol leading to formaldehyde formation while the formation of CO, CO2 (via a formate intermediate) and methyl formate occurs through three concurrent reactions from formyl species. Our findings suggest that CO adsorbed on Pt is a spectator species not perturbing the reaction kinetics, and deactivation is shown to be strongly correlated with the accumulation of formate groups on SrTiO3, which is more pronounced at high reaction temperatures. The mechanistic understanding provided here forms the basis for the further optimization of photocatalysts to increase methanol conversion and improve formaldehyde selectivity.

A triazole-based covalent organic framework as a photocatalyst toward visible-light-driven CO2 reduction to CH4.

Solar-light driven reduction of CO2 to CH4 is a complex process involving multiple electron and proton transfer processes with various intermediates. Therefore, achieving high CH4 activity and selectivity remains a significant challenge. Covalent organic frameworks (COFs) represent an emerging class of photoactive semiconductors with molecular level structural tunability, modular band gaps, and high charge carrier generation and transport within the network. Here, we developed a new heterocyclic triazole ring containing COF, TFPB-TRZ, through the condensation reaction between 1,3,5-tris(4-formylphenyl)benzene (TFPB) and 3,5-diamino-1,2,4-triazole (TRZ). The TFPB-TRZ COF with multiple heteroatoms shows suitable visible light absorption, high CO2 uptake capability and an appropriate band diagram for CO2 photoreduction. Photocatalysis results reveal a maximum CO2 to CH4 conversion of 2.34 mmol g-1 with a rate of 128 μmol g-1 h-1 and high selectivity (∼99%) using 1-benzyl-1,4-dihydronicotinamide (BNAH) and triethylamine (TEA) as sacrificial agents. Under similar reaction conditions in the presence of direct sunlight, the TFPB-TRZ COF displays a maximum CH4 yield of 493 μmol g-1 with a rate of 61.62 μmol g-1 h-1, suggesting the robustness and light-harvesting ability of the COF photocatalyst. A femtosecond transient absorption (TA) spectroscopy study shows fast decay of excited state absorption (ESA) in the COF compared to the TFPB building unit due to efficient electron transfer to the catalytic site in the framework. The mechanism of CO2 reduction to CH4 is studied by DFT-based theoretical calculation, which is further supported by an in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study. The DFT results reveal that the lone pair of electrons on nitrogen heteroatoms present in the triazole ring of the TRZ moiety help in the stabilization of the CO intermediate during CO2 to CH4 conversion. Overall, this work demonstrates the use of a metal-free, recyclable COF-based photocatalytic system for solar energy storage by CO2 reduction.

Active site-exposed Bi2WO6@BiOCl heterostructures for photocatalytic hydrogenation of nitroaromatic compounds.

Constructing heterostructured photocatalysts with highly exposed active sites proves to be an efficient strategy to improve the photocatalytic performance of bismuth-based photocatalysts. In this work, active site-exposed Bi2WO6@BiOCl (BWO@BOC) heterostructure composites based on two bismuth-based materials were fabricated by an in situ growth method for improving the photocatalytic hydrogenation of 4-aniline (4-NA) to p-phenylenediamine (PPD). BWO@BOC exhibited enhanced photoactivity for 4-NA hydrogenation compared to pure BWO and BOC. The optimal BWO@BOC composites displayed the highest conversion rate of 4-NA to PPD up to 99.3% within 12 min, with an apparent reaction rate constant of 0.414 min-1, which is 3.3 times that of pure BOC. The photoactivity enhancement is mainly ascribed to the construction of a tight Z-scheme heterostructure with improved light harvesting properties and charge carrier transport efficiency, which were revealed by optical and photoelectrochemical characterization, respectively. Furthermore, the products of the hydrogenation process were monitored by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to gain a better insight into the 4-NA hydrogenation mechanism.

Understanding the role of supported Rh atoms and clusters during hydroformylation and CO hydrogenation reactions with in situ/operando XAS and DRIFT spectroscopy.

Supported Rh single-atoms and clusters on CeO2, MgO, and ZrO2 were investigated as catalysts for hydroformylation of ethylene to propionaldehyde and CO hydrogenation to methanol/ethanol with in situ/operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray absorption spectroscopy (XAS). Under hydroformylation reaction conditions, operando spectroscopic investigations unravel the presence of both single atoms and clusters and detected at first propanal and then methanol. We find that the formation of methanol is associated with CO hydrogenation over Rh clusters which was further confirmed under CO hydrogenation conditions at elevated pressure. The activity of catalysts synthesized via a precipitation (PP) method over various supports towards the hydroformylation reaction follows the order: Rh/ZrO2 > Rh/CeO2 > Rh/MgO. Comparing Rh/CeO2 catalysts synthesized via different methods, catalysts prepared by flame spray pyrolysis (FSP) showed catalytic activity for the hydroformylation reaction at lower temperatures (413 K), whereas catalysts prepared by wet impregnation (WI) showed the highest stability. These results not only provide fundamental insights into the atomistic level of industrially relevant reactions but also pave the way for a rational design of new catalysts in the future.